Examination of the prior art yields a variety of face masks or respirators for treatment of breathed air. Generally, the masks of the prior art may be categorized into one of two classes, namely; disposable or single-use respirators and replaceable cartridge respirators.
In general, disposable masks of the prior art are made of a permeable fibrous media formed into a cup shape to fit the contour of the face of the wearer. In some masks the fibrous media is formed to fit the face of the wearer and, simultaneously, achieves a seal against the flow of toxic dusts and mists into the breathed air chamber. In other masks a nose clip is attached to the face mask and is utilized to achieve a seal around the nose area.
In the majority of disposable fibrous media masks of the prior art, breathed air treatment and filtration is achieved by air flow through most of the area of the face mask. Although this is relatively costly, since a large amount of filtration media is used to fabricate the entire mask shell in addition to the excessive between-shell cut-out waste, it is advantageous since it results in a relatively lower pressure drop across the filtration media for the same breathed air volume flow rate. Those masks still have a limited capacity and lack the ability to carry a sufficient charge of air treatment substances for the absorption of toxic gasses, fumes, vapors, etcetera in order to provide the wearer with protection in harmful environments. Thus, such disposable face masks cannot meet standards or requirements for governmental approval in such applications. For example, it is difficult to impregnate the disposable face mask fibrous media with a sufficient charge of activated charcoal granules (approximately 100 grams) to pass government requirements for paint spray, organic vapor, acid gas or pesticide applications. This is due to the limited capacity of the fibrous media for encapsulating or for being loaded or impregnated with toxic gas treatment media. In certain instances, even when a relatively thicker fibrous shell is used, the amount of charcoal encapsulated in the mask shell is insufficient for meeting the National Institute for Occupational Safety and Health (NIOSH) requirements for certification or approval for paint spray applications. In such cases the resulting mask, lacking NIOSH approval, is usually referred to as a nuisance mask.
In many cases, however, where the filtration media is impregnated with air treatment substances or is loaded with additional fibrous media, the face mask is relatively thicker and a good face-mask fit and seal are much harder to achieve. In these cases a nose clip and/or wide, low extensibility heavy duty straps are used in order to apply a high force to pull the mask against the face of the wearer. As a result, the air seal is obtained by deforming the wearer's face to conform to the perimeter of the mask, rather than deforming the mask to conform to the face of the wearer. Needless to say, such a mask is not comfortable to wear.
Therefore, a limiting factor in making single use respirators that meet NIOSH requirements is that it is very difficult to produce a fibrous media mask carrying a weight of approximately 100 grams of activated charcoal granules while maintaining the total mass of the mask within bearable limits.
Examination of prior art masks shows that the formulation of the majority of disposable masks involves heating, stretching and/or compressive compaction of the filtration media. Such processing factors may adversely influence the effectiveness of the filtration media with regard to its filtration efficiency and pressure drop. The examination also shows that, in the majority of disposable masks, the area of contact with the face of the wearer is of a fibrous nature and thus cannot provide an airtight seal similar to an elastomeric material seal as required by regulatory agencies for certain applications against toxic gasses and vapors.
In the manufacture of respirators designed for single use or for a finite period use, a significant portion of the overall product cost is the cost of the filtration media. As the cost of media (including cut out waste) increases, the competetiveness of the overall product in the marketplace suffers significantly. This is typically true in all face masks targeted to the particulate filtration applications, including toxic dusts and mists. In the majority of such masks the area of filtration media in the final product is equal to the area of the mask shell.
In the prior art, numerous products and patents are directed towards obtaining an effective air-tight seal between the perimeter of the mask shell and the face of a wearer. In certain instances a polymeric bead, rim, flap, or their combinations are added at the perimeter of the fibrous shell face mask. Except for use of a thin rim of impermeable closed cell elastomeric material or foam around the perimeter of the face mask in the zone in contact with the face of the wearer, examination of prior art masks and patents has shown no suggestion or use of impermeable polymeric foam materials in the basic shell comprising the body of face masks.
On the other hand, replaceable cartridge masks of the prior art are generally comprised of an elastomeric face piece designed to fit the face of the wearer and achieve an air-tight seal with the face of the wearer. The elastomeric face piece is usually fitted with at least one opening to receive a detachably attached cartridge for treatment of the breathed air. The elastomeric face piece is also usually fitted with a one-way exhalation valve.
In order to achieve and maintain an air-tight seal around the perimeter of a cartridge, the mask shell is stiffened either through ribbing or through the use of increased material thickness, particularly around the cartridge receiving opening. Hence, the face mask is generally made of a heavy construction and thus feels heavy on the face of the wearer. As an example, a replaceable cartridge mask of the prior art was weighed and yielded the following data. The total weight of the basic face mask shell with mounting straps and two replaceable activated charcoal granule filters is 327 grams. The weight of the two filter cartridges is 183 grams. The ratio of the weight of the mask functional components (filters) to the total mask weight, R=182/327=0.56.
From a mask wearer's comfort standpoint, while a mask is performing its intended function, it may be concluded that it is desirable to maintain the ratio R as high as possible, particularly for masks requiring relatively heavy functional components (filters). In such cases, as R approaches its limit value of 1, the wearer's discomfort is minimized.
Generally speaking, however, NIOSH approved masks which utilize detachably attached, replaceable cartridges are costly since a sizable initial capital investment has to be made for the durable face mask shell. Other indirect costs include the cost of periodic shell cleaning, sanitization, testing for cuts, cracks, leakage, etcetera and storage. In certain work places individuals using such durable face masks prefer or require that no other co-worker may use the same face mask shell at any other time. This is usually done for the prevention of transmittal of communicable diseases through breathing contaminated air or through skin or saliva contact with a contaminated mask shell. In this case certain face mask shells are numbered and designated for use only by certain individuals.
Additionally, in certain applications, for example in asbestos fiber contaminated environments, the subsequent shaking off of the mask shell after use contaminates the clean environment. In such cases it is desirable to dispose of the entire mask shell and air filtering cartridges after each use. Such disposal is costly since a major expense is incurred in the cost of the mask shell. On the other hand, recently adopted government regulations disallowed approval of conventional disposable face masks for use in asbestos fiber contaminated environments.
Also, most durable masks, particularly approved ones, require a high force to pull them against the face of a wearer in order to achieve an effective seal with the face of the wearer. When such masks are made of a heavy duty construction the need also arises for head-top band in order to prevent the mask from falling off the face of the wearer and to maintain a complete seal with the face of the wearer. Such head-top band is usually branched off the above-the-ear band and is placed on top of the head of the wearer of the mask. Such a head-top band is particularly undesirable when the wearer's head top is bald at the location of the head-top band.
As may be concluded from the above, there is a need in the art for an inexpensive, flexible shell that is light weight, single-user (single or repeated use) face mask which fits around and achieves a complete air tight seal with the face of the wearer. Such a mask should have a fit and seal that are comparable to the fit and seal obtained with presently available elastomeric face pieces, while feeling light and thus relatively more comfortable, and being able to carry a charge of air treatment or filtration media and/or devices sufficient to perform the desired protection against specific environmental hazards.
The needs of the prior art are met by the face mask taught and claimed herein. The novel mask bridges the gap between unapproved disposable masks and expensive, approved replaceable cartridge respirators. This mask features a light weight, closed cell foam mask shell with one or more holes through its central area, and one or more pieces of inexpensive sheet filter material that are held over said holes and in contact with the mask shell by a plastic retainer.
The above needs of the prior art are met by the present novel face mask which can be non-disposable or disposable, which filters particulate matter, noxious and poisonous gasses from inhaled air, which is of relatively light weight, which is soft and flexible and forms a good seal to a wear's face around the nose and mouth without the need for tight elastic straps, which does not deform the face of the wearer to accomplish a good seal, which is comfortable to wear for extended periods of time, and which is relatively inexpensive. Such a face mask is a viable alternative to prior art rubber shell masks so that each worker may have their own reusable mask or may dispose of a mask after a single use.
The primary embodiment of the novel mask has an outer shell that is thermoformed of cross-linked, closed-cell foam sheet. The foam shell is impermeable to air while being soft and flexible, and having good shape retention and elasticity. The center area of the shell is perforated with multiple holes to permit inhaled air to pass through the otherwise air impermeable shell and through the filter liner(s) positioned inside or outside the mask over the holes. This mask shell is stiff enough to support a variety of filter liners, either singly or in combination, ranging from a simple fibrous filter liner for filtering dust or mist, to an activated charcoal impregnated fibrous sheet liner for filtering noxious and poisonous gasses and other dangerous materials. The filters may be removably retained to the inside or to the outside of the shell over the holes by a force fit retainer or by clips that are both easily removed to replace the filter liner. The removable filter liners may also be attached to the inside or outside of the shell by self adhesive strips around the periphery of the filter liner. The filter liners may also be thermobonded or otherwise permanently bonded to the inside or outside of the mask over the holes to make a disposable version of the mask. When filter liners are attached to both the inside and to the outside of the shell over the holes, the outer liner serves as a pre-filter, and the inner liner serves as a post-filter.
A one-way exhaust valve may be mounted through the wall of the foam mask shell to vent exhaled air. The exhaust valve is located in a position where it does not interfere with the filter liner(s).
In an alternative embodiment of the invention the basic shell may be formed of two parts. The periphery of the shell which contacts the face of the wearer and makes an air tight seal thereto, and to which straps would attach, would be formed of the air impermeable foam material. Attached to the shell periphery by thermobonding, adhesives or other methods is a piece of air permeable foam that eliminates the need for the holes in the primary embodiment of the invention. The filter liners are still attached to the inside and/or the outside of the mask over the air permeable foam material. The liners are attached permanently for a disposable mask, and are removable as previously mentioned for a reusable mask.
In still another embodiment of the invention the closed cell foam material from which the mask shell is thermoformed is made up of a layered material. The outermost layer that is on the side mask shell that contacts the face may be of a material that permits more comfortable wearing of the mask, or that is best to reduce chafing or hypoallergenic effects. The other layers may be chosen for shape retention, aesthetics, or for many other reasons.
In another embodiment of the invention one or more filter layers are not attached to the inside and/or the outside of the foam shell but, rather, one or more filter cartridges are attached through the wall of the shell. The cartridges may be detachably fastened to collars that mount through and are fastened to the foam shell.
In yet another alternative embodiment of the invention the mask shell may not be formed of closed cell foam, but may comprise a shell that is fabricated by thermoforming a sheet of commercially available, synthetic fiber, nonwoven, filter material. The shell so formed may be cup-shaped. During forming a piece of a fibrous sheet material impregnated with activated charcoal or other filtration substance is thermobonded or otherwise fastened to the inside of the mask but not overlapping the edge of the mask. In this manner the filter material forming the basic mask shell also does pre-filtering, and the filter liner affixed to the inside of the shell is the post-filter.